Flagg

How many pounds reduced, is equal to one HP Gained?? I have heard numbers ranging from 5-15lbs?

I guess that number would keep changing as you removed weight from your car? Does anyone have a good way to figure this out?

Flagg

Cupcar

Current weight to HP ratio=the value of 1 HP in pounds at current weight and horsepower.

For example, if a 2000 pound car had 200 HP the ratio would be 10 pounds per horsepower.

Therefore, removing the first 10 pounds would equal one horsepower for the example above.

The next horsepower would then be worth 9.95 pounds since 2000-10=1990 pounds 1990/200=9.95. Another way to look at it, for a 10:1 HP/wt ratio we would only need 199 HP, 1 HP less in our 1990 pound car.

The lighter the car gets, the less you have to remove to equal 1 HP; less is more in action!!!

Flagg

CupCar - Thanks - this makes a lot of sense. Sounds like you have to take some major weight out of the car before you would feel too much of a difference.

Doing that calculation for my car I think would need to take out about 11 lbs for the first horspower.

Thanks, Flagg

Marc Shaw

Okay, so instead of a 3.8 upgrade, I'm gonna save up for liposuction!

Marc

bhensarl

That's the beautiful thing about weight reduction, it's very cost efficient. I mean look at all the stuff you can get rid of, and for free! First aid kit, reflector, carpets, rear seats, pax seat, A/C... Just depends how hard core you are, I guess.
Brian

garrett376

Not only is removing stuff "free", but the lighter the car, the better gas mileage, less tire wear, less brake wear, it stops faster, accelerates faster... it's the gift that keeps on giving!!

(this coming from someone with bloody knuckles from recently pulling out the engine sound pad!!)

tonytaylor

I don't think this is the case. Take 50kg out and you can really feel the difference. There are a few big ticket items that easily accomplish this.

I'm not sure removing stuff is "free" since you often replace heavy stuff with expensive light stuff and deletions cost in comfort etc.
I would agree that weight reduction improves performance overall though with decreased braking distances, higher corner speeds and better acceleration. The other point is that improved hp/weight ratio acheived by weight loss is 100% reliable in that while a highly stessed high power engine is more likely to break or run less than optimium than a lower powered "stock" engine a lightweight part is unlikely to increase in weight, and as Garrett says, there is less wear and tear on the rest of the car.

Jerseybean

I guess that spare tire that Im carrying around right now could use a little reduction, I hear Dr. Atkins calling my name...

TB993tt

The way I like to work it out is to calculate how the power to weight ratio changes as the weight is removed. For example car weighs 3300lbs and produces 500hp, power to weight ratio is 500/3300x2240=339 bhp/ton
If one removes say 100lbs in weight from this car, the new power to weight ratio is: 500/3200x2240=350 bhp/ton
Now to work out how much hp you have "won" by reducing the weight:
350x3300/2240=516bhp - so to get your 3300lb car to have the same power/weight ratio as your 100lb lighter car you would have to add 16hp - or you have "gained" 16 bhp by taking off the 100lbs on THAT specific car with THAT specific engine.

Cupcar

The real beauty of mass reduction is that it improves every force related performance variable- cornering and braking as well as acceleration.

All other variables being equal (tires, brakes, suspension etc), a 400 HP /4000 pound car will generally lose to a 200 HP/ 2000 pound car on the race track even though the power ratios are equal.

Flagg

This is a very cool comparision, and it makes a lot of sense.

Even if acceleration is equal with the 400 hp car, you can see that the weight would put an added toll on the suspension and braking.....and that the lighter car with 200 horsepower would probably win the race.....

Time to give some thought to what I could pull out of my car..........You could probably feel a real difference with 100lbs. Problem is that I do not want to strip everything out of the car, and remove all the comfort and style out of the car.

My RSA has a roll bar, Fire Ext, Shock tower brace, is lowered, Chip, bypass pipe, Alum dead pedal and gas pedal, rotated tach, etc........But I have not ripped the carpet out or anything serious like that. I kind of like the edge that the car has now. Fast, well set up, but still enough comfort that my wife will still ride in it

Perhaps one day I will pull that rear deck (I have a CD changer installed on the underside or i would do that right now), change out the seats, Carbon Fiber Hood, strip the carpet up front, etc. But try to keep the creature comforts of the cabin mostly in tach...........

Flagg

Cupcar

The key with weight removal is to lower the so called "polar moments". This means that weight removed far from the center of gravity such as from the top (sunroof) and ends (bumper beams) of chassis is more effective than that close to the center of gravity. The most effective is removal of unsprung weight, but here the holy grail is rotating and unsprung weight-wheels, tires and brake discs, here the rule applies to distance from center of rotation. Weight removed from the tire tread itself is most effective while weight from the wheel center is less effective.

springer3

Mass affects inertia only (F=mA). Wind resistance consumes the larger percentage of the available power as speed increases. Assuming equal frontal area and drag Cx, the 400 HP/4000 lb car, and the 200 HP/200 lb car will accelerate off the line with identical acceleration. The more powerful car will be much faster as wind resistance becomes a factor. I want the 2000 lb car with the 400 HP engine!

Flagg

How fast do you have to be going for wind resistance to make a big enough difference to give the heavy car the advantage. 100? 150?

Flagg

Cupcar

If one could control all other resistance and power variables to perfection, it would be shown that wind resistance would be an issue from the start.